Process for preparing phosphonates



United States Patent No Drawing. Application June 14,1954

Serial No. 436,731

6 Claims. (Cl. 260-461) This invention relates to a method for converting a phosphorous compound, e,g. phosphite or a phosphorous acid, to a phosphonate, particularly methane phosphonates, by reaction with an ester of a phosphoric acid, particularly selected from the methyl esters.

Methane phosphonic acid derivatives have been made by pyrolysis of dimethyl phosphite ,alone but not by reaction of the phosphite ester or of phosphorous acid with an ester of another oxy-acid, particularly such as a phosphoric acid.

For the present invention, it was found that "(the methane'phosphonic acid derivatives can be obtained by reaction of phosphorous acid or methyl phosphites with methyl esters of phosphoric acid, and the yields of desired product are better than in the absence of the methyl phosphate esters. p

The desired methane phosphonic acid derivatives are represented by the following general formula:

0 CH;-'P0R1 .O-Rz wherein R and R stand for hydrogen, methyl, or. a phosphorus-containing radical. Specific .examples of these derivatives are:

V OH3POH (Em-$ 0011.

OH .OH Methane phosphonic Mono methyl methane acid phosphonic acid iPyro methane phosphonic acid CHa-P "Trimeric methane phosphonic acid ,anhydride EXAMPLES was stopped after a period of from 10 minutes to about 60 minutes. The trimethyl phosphate gave the quickest V H P 0 =Phosphorous acid 2,908,708 Patented Oct. 13, 1959 reaction for same extent of conversion at a given temperature.

The reaction product was cooled and Weighed, then analyzed for P and P methane phosphoric acid, and total phosphorus content.

In general, the reaction products are clear, Colorless liquids with densities above 1.0. On extended cooling at temperatures below 100' C., the products become solidi fied. On reheating the products are reliquefied. The products are water-soluble.

The product obtained and described is useful as such, without further purification.

Other specific examples of the desired derivatives of the methane phosphonic acids shown are the dimethyl ester derivatives.

Improvements in yields of the desired methane phosphonic acid derivatives obtained by using the process of the present invention are shown in the following Table I.

Table I [All samples heated slowly in pairs to reaction temperature, 270 0.]

MMHP=Monomethyl phosphite DMHP=Dimethyl phosphite MP=Mixed monoand di-methyl phosphates Me l 0 =Trimethy1 phosphate P Phosphite phosphorus P =gndzcsired phosphate phosphorus of phosphate and phosphine pro uc s.

The summarized data in Table I shows in the duplicate experiments C and D that the presence of an equal amount of trimethyl phosphate did not affect the percentage of I I PO decomposed but changed the course of this decomp'osition from 100% undesired products to 97% desired products methane phosphonic acid derivatives,

In the pair of experiments G and H, mixed monoand di-methyl phosphates caused H PO to yield selectively 62% of the desired methane phosphonic acid derivatives instead of giving 100% conversion to undesired products.

The mixture of monomethyl phosphite and phosphorus acid referred to in the Table I as Sample A and Sample E contained by analysis of their aqueous solutions about 82 mole percent total phosphites including 52 mole percent monomethyl phosphite, 30% H PO and 1% dimethyl phosphite. These mixtures were obtained as bottoms in the distillation of crude dimethyl phosphite (DMHP).

In the absence of the added methyl phosphates or V similarly reacting esters, there is a low yield of only 20% of the desired products per pass or per fresh batch. In the duplicate experiment B, the added trimethyl phosphate raised the conversion to from 37% and :changed the yield to 82% of desired products per pass, which is a considerable advantage. Similarly, in the experimentsE and F the mixed added methyl phosphates enhanced the yield of desired products although under these conditions they did not change the total phosphite conversion level very much.

It has been found that dimethyl hydrogen phosphite (DMHP) when pyrolyzed initially forms no appreciable amount of phosphates. As the pyrolysis reaction proceeds, substantial amounts of material which analyzes in aqueous solutions as monomethyl phosphite (MMHP) and H PO form. Consequently as the pyrolysis is continued these are converted into more undesired products, phosphates and phosphines. Accordingly, it is beneficial to add methyl phosphate esters at some stage of the pyrolysis for conversion of phosphites to the desired phosphonate derivatives.

In the examples given in the Table I, extraneous phosphate esters were added to the phosphite pyrolysis feeds to ascertain the specific ajfects of the phosphate esters. In an improved embodiment, the present invention contemplates the production of dimethyl phosphate along with dimethyl phosphite by judicious addition of POCl to the PC1 feed to methanol to form such a mixture.

Another embodiment of this invention involves the addition of trimethyl phosphate or similar ester to the reaction mixture in the pyrolysis of dimethyl hydrogen phosphite at the proper time for obtaining maximum yield.

In the staged recirculating pyrolysis of DMHP this invention envisions the addition of the methyl ester to a point near the end of the pyrolysis. For example in an apparatus containing two circulating units the ester is added to the effluent before or during addition of the efiluent to a final pyrolysis state.

The use of methyl esters such as trimethyl phosphate does not exclude the use of BF or other such catalysts. In fact where trimethyl or dimethyl phosphate is added to DMHP in a pyrolysis reaction, BF may also have been added. One attractive process involves the use of BF;, to catalyze the desired reactions at the beginning and the addition of methyl phosphates to give better yields during the last half of the reaction when large amounts of unconverted phosphites such as monomethyl phosphite and H PO are present.

In staged pyrolysis such as that above it is advantageous to use methyl phosphates in the higher temperature, second stage. B1 is especially beneficial at lower temperature early stages. 7

Study of the action of trior dimethyl phosphate on phosphorous acid indicates that ester interchange may occur. This concept does not limit the invention, however, and is not meant to indicate that monoor dimethyl phosphite is essential to the production of methane phosphonic acid derivatives.

While trimethyl phosphate is a more desirable methylating agent, it costs more than dior monomethyl phosphate. On the basis of equal methyl content it may be no more desirable. One view holds that the last methyl, i.e., the one visualized as held by the weakly acid POH, is the reactive one. On this basis the trimethyl phosphate has two methyls in reserve but the active methyl is the same as or similar in activity to that in mono- 4 methyl phosphate. This concept is not to be construed as limiting the invention.

The temperature required for the above-discussed methylations ranges between an upper limit of about 350 C. and a lower limit determined by that resulting from spontaneous reaction of the cold reagents. It is believed that C. to 275 C. is a preferred operating range. The amounts of methylating agents used is of course influenced by many considerations including the feed composition, catalyst, temperature and the economics of the particular reaction. Excess trimethyl phosphate of course would give the maximum yield and fastest reaction according to the present interpretation of the data.

Phosphates are desirable agents since present processes for phosphite pyrolysis include systems for handling these pyrolytic products. Borates are attractive because of the possibility that they might be regenerable with methanol treat to give volatile trimethyl borate.

In special cases other methyl esters might be more desirable.

It is envisioned that mixtures of methyl esters might be especially interesting. Methyl chloride in methyl phosphate or borate is suggested.

Products of this invention may be employed in preparing fuel, lubricating oil, and grease additives, detergents, fire retardants, insecticides, and plasticizers. The methane phosphonic acids undergo reaction with alcohols, esters, salts, bases, as well as with halogens and nonmetallic halides.

In addition to the preceding ideas many others will now be obvious to those skilled in the art.

The invention described is claimed as follows:

1. Process for preparing a methane phosphonate which comprises reacting a phosphorous compound selected from the group consisting of phosphorous acid and methyl esters thereof with a methyl ester of a phosphoric acid.

2. Process for preparing a methane phosphonate by reacting a phosphorous acid and a methyl ester thereof with a methyl ester of a phosphoric acid.

3. Process for preparing a methane phosphonic acid and methyl esters thereof which comprises reacting a phosphite with a methyl ester of a phosphoric acid.

4. Process for preparing a methane phosphonic acid and a methyl ester thereof which comprises reacting a phosphorous acid with a methyl ester of a phosphoric acid.

5. Process for preparing methane phosphonic acid and a methyl ester thereof which comprises heating a mixture containing phosphorous acid and mono-methyl phosphite with a mixture containing monoand dimethyl phosphate to temperatures in the range of 100 to 350 C.

6. Process for preparing a methane phosphonic acid and methyl esters thereof which comprises heating a mixture containing phosphorous acid and mono-methyl phosphite with trimethyl phosphate to temperatures in the range of 100 to 350 C.

No references cited. 

1. PROCESS FOR PREPARING A METHOANE PHOSPHONATE WHICH COMPRISES REACTING A PHOSPHOROUS COMPOUND SELECTED FROM THE GROUP CONSISTING OF PHOSPHOROUS ACID AND METHYL ESTERS THEREOF WITH A METHYL ESTER OF A PHOSPHORIC ACID. 